1. Field of the Invention
The present invention relates to a process for producing attractive text images with improved smoothness in diagonal lines from character fonts and binary image data obtained by an image scanner or other image reading device. There is a broad range of applications for this process displaying fonts in a video display, video printers, text file display devices, facsimile display devices using liquid crystal displays, and other image display devices.
2. Description of the Prior Art
Laser beam printers and other extremely high resolution page printers offering resolutions of 400 dpi (dots per inch) and greater have become essential office equipment in the last few years as the technologies enabling hard-copy output of sharp, attractive text and graphics have become commonly available.
The text fonts used in these devices typically use bit-image fonts or vector (outline) fonts stored in a large capacity ROM. In a bit-image font each character is defined with an extremely large number of dots and the complete character set (font) is stored in the ROM. In vector fonts, each character is defined by vector coordinates and the characters can be scaled to the selected size by applying a mathematical algorithm to dynamically generate the bit image viewed on screen or paper. Extremely sharp, well-defined characters can be printed using a high resolution printer, and smooth contours can be obtained in virtually any font size using a scalable font. Scalable fonts have therefore become the mainstream in high resolution imaging devices.
The WYSIWYG (What You See Is What You Get) interface has also become the standard for personal computer user interface design, enabling the user to see the same image on screen and on the printed page. Advancing this WYSIWYG interface one step further, scalable fonts are gradually replacing bit image fonts in the processes used to generate on-screen displays.
When outputting text to a video display, however, it is difficult to achieve a text display with smooth diagonal lines in various font sizes because the resolution of even high resolution displays is a fraction of the resolution of a high resolution printer, and be necessity the characters are formed using fewer dots. As a result, scalability is the only characteristic of outline fonts that is currently used to generate on-screen text displays.
When displaying Chinese characters or Japanese kanji characters, the display is typically limited to 16-24 dots per character. This small number of dots makes it extremely difficult to display smooth characters free of jagged lines. It is difficult to display these characters smoothly even when using outline fonts because of the small number of dots, and the quality of the bit images generated from these outline fonts is lower than the quality of bit-mapped fonts manually designed to the same point size. The drawback to using bit-mapped fonts as semi-scalable fonts is that bit maps must be designed for each point size, and the memory capacity required to display large point sizes increases dramatically.
Whether using bit-mapped or outline fonts, however, it is not possible to display smooth contours with a line width smaller than the physical size of the display pixels, and high definition display of small point size characters is therefore not possible.
While methods of making these jagged diagonal lines less conspicuous by blurring text and images using a low-pass filter (LPF) or other band width limitation process have been proposed, these processes also blur horizontal and vertical lines in which there is no jaggedness. The result is an image or text display from which sharpness and definition have been blurred out.